Kurgantaite CaSr[B5O9]Cl·H2O

- Crystal Data: Triclinic. Point Group: 1 . Forms fine-grained nodules, to 4 cm; also as spherulites of crystals with wedge-shaped terminations, to 0.7 mm.

Physical Properties: Cleavage: Present in two directions. Fracture: Uneven. Tenacity: Brittle. Hardness = 6-6.5 D(meas.) = 2.99(1) D(calc.) = 3.07(1)

Optical Properties: Transparent. Color: Colorless to white, light to dark yellow-orange to orange. Streak: White. Luster: Vitreous. Optical Class: Biaxial (+). α = 1.637(1) β = 1.638(1) γ = 1.675(1) 2V(meas.) < 10° 2V(calc.) = 19(19)° - Cell Data: Space Group: P1 . a = 6.573(1) b = 6.445(1) c = 6.369(1) α = 60.995(2)° β = 61.257(2)° γ = 77.191(2)° Z = 1

X-ray Powder Pattern: Chelkar, Kazakhstan. 2.92 (100), 3.22 (90), 2.84 (90), 5.69 (80), 2.79 (80), 3.13 (70), 2.14 (70)

Chemistry: (1) (2) (3) CaO 14.69 15.06 16.19 SrO 26.43 26.34 25.51 B2O3 45.31 44.93 46.29 Cl 9.58 9.22 9.22 H2O [4.69] [4.65] [4.79] -O = Cl 2.16 2.08 2.08 Total 98.54 98.12 99.92

(1) Kargan-tau, Kazakhstan; electron microprobe analysis, H2O calculated from structure refinement; corresponding to Ca1.01Sr0.98[B5.02O9]Cl1.04·H2O. (2) Nepskoye, Russia, electron microprobe analysis, H2O calculated from structure refinement; corresponding to Ca1.04Sr0.98[B4.99O9]Cl1.01·H2O. (3) Penobsquis deposit, New Brunswick, Canada; average of 3 electron microprobe analyses, H2O calculated; corresponding to Ca1.08Sr0.93[B5O9]Cl0.98·H2O.

Mineral Group: Hilgardite group.

Occurrence: In marine evaporite salt deposits and salt domes.

Association: Sylvite, halite, boracite, anhydrite, gypsum, magnesite, quartz (Kazakhstan); hydroboracite, boracite, walkerite, veatchite, szaibélyite, pringleite, congolite, a clay-group mineral (New Brunswick, Canada).

Distribution: In western Kargan-tau, Inder uplift and from Chelkar, Caspian region, Kazakhstan; in the Nepskoye potassium salt deposit, near Ust’-Kut, Irkutsk district, Siberia, Russia. In the Penobsquis evaporite deposits, 12 km NE of Sussex, New Brunswick, Canada.

Name: For the region, Kargan-tau, Kazakhstan, that produced the first specimens.

Type Material: A.E. Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia.

References: (1) Pekov, I.V., E.V. Lovskaya, N.V. Chukanov, A.E. Zadov, V.N. Apollonov, D.Yu. Pushcharovsky, O. Ferro, S.A. Vino-gradova (2001) Kurgantaite, CaSr[B5O9]Cl·H2O, revalidation of the mineral species and new data. Zap. Vseross. Mineral. Obshch., 130(3), 71-79 (in Russian, with English abs.). (2) (2002) Amer. Mineral., 87, 1510-1511 (abs. ref. 1). (3) Grice, J.D., R.A. Gault and J. Van Velthuizen (2005) Borate minerals of the Penobsquis and Millstream deposits, Southern New Brunswick, Canada. Can. Mineral., 43, 1469-1487.

Mineralogical Society of America Handbook of Mineralogy Revised 3/2/2015